Acceleration responsive devices



June 28, 1960 E. v. HARDWAY, JR 2,942,456

ACCELERATION RESPONSIVE DEVICES Filed Sept. 10, 1954 1 NVENTOR ATTORNEY,

iinited States Patent" O aconrnnrtrron nnsroNsrvn nnvrcns Edward V.Hardway,v.lr., Goochland County, Va., as-

signor, by mesne assignments, to Robertshaw-liulton Controls Company,Richmond, Va., a corporation of Delaware meti sept. 10,1954, ser, No.455,297` y 4' claims. (el. 'la-.71)

This invention relates to acceleration responsive devices andparticularly to such devices which may be constructed at unusu-ally lowcost and which are characterized by accurate, repeatable response over awide range of vibratory frequencies and acceleration values.

There has long been a need for a dependable acceleration responsivedevice with a mechanical output suitable for acceleration measurementand the actuation of switches or other control apparatus. In particular,users of turbines, compressors, jet engines, automatic machine tools,and the like require some automatic means for actuating a warning systemor shutting down a machine when excess vibration occurs.V rPhe problemis of particular importancefiwhen unattended machines .of great valueare involved. Failure to detect an increase in vibration may frequentlyresultin costly damage or, in some instances, loss of life. An exampleof the latter is that tof detecting excess jet engine vibration onaircraftV in flight. Y

In the past, numerous acceleration 'responsive systems have beenproposed for such applications. The most widely used combinations employsome form of pickup or transducer for continuously sensing the vibratoryvelocity or acceleration, a high-gain ampliiier, and a relay or sometype of Vindicating or recording device. Such systems are complicated,very expensive, and frequently require more maintenance than theequipment they are installed to protect; Velocity and accelerationtransducers for vibration measurements all require some degree ofrelative motion between'the instrument case and the mass or inertialelementto function'. This requirement imposes severe limitations on thefrequency response and limits the energy converted necessitating highgain ampliiicationof the electrical output. Suchv limitations appearunavoidable in research applications vwhere the entire vibration Waveform is of interest, but they severely restrict the applicability ofsuch.j equipment to extensive industrial use.

An object of the present inventionis to provide an immeans readilyadaptable for'directmechanical actuation of electrical switches, valves,visual signals, sounding d'evices,andthelike. "j y l ,f f

In general, acceleration responsive-devices constructed in accordancewith theinventionrinvolve a supprtfsfuch as a case, an inertiamnitandamagnetic couple*comi prising a permanent magnet anda magneticallysoftbody (or a second permanent magnet): elementgofthe.'

couple is rigidly fixed to the inertia unit and the other Ice 2,942,456

element to the support. The inertia unit is attached to the support bymounting means which coacts with the magnetic couple to initiallyrestrain the inertia unit against any motion relative to the supportwhen the magnetic couple is engaged. This mounting means accuratelylocates Ythe relative position of engagement of the elements 'of themagnetic couple and constrains the inertia unit to one degree of freedomin movement of the inertia unit relative to the support when themagnetic couple is disengaged. Adjustable biasing means is provided toapply to the inertia unit a biasing force tending to disengage themagnetic couple.

When the magnetic couple is engaged, the inertia unit is constrained tokmove -with the support and thus is subject to the same acceleration asis the support regardless of the frequency, rate of change, or amplitudeof such acceleration. The setting of the adjustable biasing meansdetermines the particular acceleration level which will be effective tocause disengagement of the magnetic couple. Thus, near the actu-atingpoint, the forces involved are nearly in balance,` yet all components ofthe device including the inertia unit and the support move together as arigid unit. Occurrence of the predetermined acceleration level selectedby adjustment of the biasing means causes the inertial and biasingforces to exceed the restraining force of the magnetic couple so that aslight gap or increase in gap occurs in the `iiux path of the magneticmeans which, in turn, causes a large unbalance of forces affectingtheinertia unit, resulting in disengagement of the magnetic couple. Uponsuch disengagement the substantial potential energy available from thebiasing means is released and may be used to actuate a switch or otherdevice.

Particular attention must be given to maintaining the 'entire structureas a rigid unit until the selected acceleration level occurs. Themounting means for the inertia unit and the magnetic couple are arrangedto insure an identical `condition of engagement of the magnetic coupleafter each operation so that no change will occur in the restrainingforce of the magnetic couple during engagement or between successiveengagements. The mounting means should be constructed so as to allowonly one degreefof freedom of the inerti-a unit in motion near the pointof engagementv of the magnetic couple and in a direction to engage ordisengage the couple. It should' Y allow substantially no motion in anyother direction. At-

tention must be given to the reduction of compliance in the support,mounting means, magnetic means, and inertia unit to prevent vibratorymodes of resonance in the desired usefulA frequency range, orsensitivity changes resulting from iiexure.' I have found that byfulfilling the above requirements precise results may be obtained over awide frequency range using relatively inexpensive components, and thatthe biasing means may be calibrated to enable the user to quantitativelyselect the acceleration level for operation of the device orquantitatively deter-A mine the level of an unknown acceleration.

In order that the invention may be understood in de tail, reference ismade to the accompanying drawings which form a part of thisspecification and wherein:

Fig. l isa side elevational view, partly in vertical section, of apreferred embodiment of the invention;

Fig. 2 is a plan view of the inertia unit, and its mounting means,employed in the device of Fig. l; F Fig. 3 is a vertical sectional viewtaken-on line 3 3 ig. 1; t

Fig. 4 is a perspective view, reduced in scale, of the dev-ice of Fig.1, and Y f.

f Fig. 5 is a detail view, in vertical section, of a, modi-A liedembodiment of certain parts of the device of Fig. fl. v

Referring now to the drawingsiu detail, it will beseen Patented- .iuneas, 196e 3. comprises a base 101 to which is rigidly connected a sup-;lagt including a base member'102f and end plates 103 and The inertiaunit of this embodiment comprises a memf ber 105 fabricated ofmagnetically soft material andconstitutingA 'a material mass. over andrigidly secured to' linking means j comprising spaced Vparallel shafts'106`an'd '107,' The inertiajuntis' mounted by means of a substantiallyfrictionless pivot including a iiat' sheet-likev element which jmay takethe# form `of afleafy spring 109' tothe loppositeV faces of Vvwhicl'rarerigidly secured blocks 1.00 and 110, the blocks being offsetonefromthe other and havingftheir adjacentcorners 131 having a collar132 engaging a coil spring 133 supported .by bracket 114. Spring 133normally urges plunger 131 upwardly so that the upper end thereof isexposed exterior ofthe casing, as shown. Upon .def pression, againstAthe force of spring 133, the lower end of plunger 131 engages inertiamember 105 to pivot the same downwardly intoengagement with magnet 112.In order to" seal thelopening in casing 12S vwhich accommodates theplunger I provide a felt -washer 134, as shown.

in substantial alignment. Preferably, the adjacent corner fl portions ofthe bloeli's 103 and 1 10are slightly oyerlappedgj as shown, andthe'ccrner of block 108 nearestbloeit T110A is rounded, as seen at111,7in order to provide' for rock-` ing motion relative tospring 109.Shafts 106 and 107.

Aextend through and are rigidly securedto the upper hloclt 108, -So thatblock' 10S' is included in the inertia unit', Lower block 110 issecurely bolted to base member-$102, as shown.

Disposedlbeneath member 105, with pole faces upward,

and rigidly secured to base member 102 is a permanent` magnet 112V whichcoacts withmember105 to .form a.

rrxag'neticV couple. A second permanent magnet 113,k dis-.- posedaboveblock 105 with its pole faces facing the same, isv rigidly securedto abracket 114 bolted at one .end to' upright 104 yand at the other end .apin 115 extending upwardly from `the member 102. It willbe noted-"thatthe inertia member 105-is 'free-toimove in a plane substantial-- ly atiight angles to base plate .101.hetween magnets 112- and 113,but isrestrained against movement.inganyotherv direction.

Rigidly seeured'to the top; face ofinounting:

Vmotion allowed the. inertia unit.

vsuitable, bracket 135 is provided to position washer 134, to act as aystop'forv collar'132", and to aidin positioning the inner Vend ofelectrical cable136. The conductors of cable 136 are led to switch 120and connected. thereto 110 are attached tov leaf spring 1'09 by means ofmachine screws or the like, and the corners of the leaf spring are thensoldered to the adjacent surfaces of the blocks. Both ends of spring122'are soldered lto elements '118 and 123, respectively`,rso'thatthespring may not sliift laterally.`

Members 102' and 128 Yarea-igidly secured by vmeans-of closelyspacedmachine screws.vk When .the device is oon'- structed in this manner, andinertia'unit 105 is inV engage- Y ment with magnet -1-12,any'acc'eleration eiecting the case will be imparted to the inertiaunit,V and the inertia unit will Vvbe free from transitory rvibratorymotion which rnightarise from movementV of otherparts within the is a.substantially inflexiblemetal plate 116'; having a .for-" Y. wardextension 117 and arearwardextension 1-2i8., Ex

tensiou-`117 engages the 'tipjof reciprocable operating pin i 119 ofaconventional snap switch 120. Y The switch. .13l20 is mounted betweenshafts106 and 107 Vbyn'1ear1s'0'i ai, U-shaped bracket 121 boltedtomember 102.V

The -moving system of the deviceis'biased means;

of a coil spring l12.2 havingv Vits'loiwer end rigidly hired, as.. bysoldering, 4to extension 11S. Spring 122 .should preferably-be of f ullyhardlberylliumfrcopper .wire .or eqiva.. lent high quality spring..material substantially .free from;

drift and hysteresis within the working rangeof'the spring..

device.

Y lMounting meansl for the inertia-unit, comprising blocks 108 andv110Vand leaf spring 109 constitutes a substantially f {frictionless pivotcapable of constraining the inertia unit to one degree of freedominmotion relative tothe support,

such movementbeingl substantiallyperpendicular to the magnet polerfaces.Sinceethe adjacent corners-of blocksr108 and 110 overlap, and sincebiasing spring 122 actsinr adirectionurging blocks 108and5110 toward.each other,

- it willJbe seenthatthis mounting .means is free,V from any" The upperendof spring ,121-2l is' rigidlyzsecured to.' acu`p1123l, i in which isjournalledtlriefree end of van adjustingscrew; f

.124, The adius'tingsscrewis threaded .into .a suit/able look;-` nut 125rigidly iix'ed' toa mounting'bracket i126 .attachedA to upright .103.

' Afelt washer127 isldis'posed between.,

the upper surface ofbracket .12`6fand Vthe top` of 'a'. casing member12S which.enclos'cs",theoperating,rnechanisrn'ofH therdevice.l Theetposeder of adjus'tizug.,screyviY 1241s provided Awith a head'f12tlwhich, as ,seenA lacing. .dalla provided v'vjith a screw driverslotwhichVs'eryebs asfasuitablef pointer f 'ofcooperation witha calibrated d 1'A130.1

n With inertia member ltfa'finengagenztentA faces Iof permanent'magnet.112, head toV adjust the compression of Vspring 122,. so applying `aldownwardly actingrbiasing' force' .on extension/11118* and Y tending toirotate the bloclg .103 ina sense 'biasing theiiie'rtfiaV unit away frommagnet 112' toward magDe'VYl-UPQT Aoccurrence of a predetermined caseacceleration,Y selected by adjustment ofpthecompression ofspring"122,jferrfo magnetic inertia element 105 willbe freedfrom'magnet' 1`12'and pivoted upwardly into Contact with latchin'gv'inagnet 113. Such'pivotalmotion will cause actuationbf switchV120byreason-of pressure applied to,` actuating element 119 .byextension 1170i plate 116. Since spring"y 12.2` now aidsthe`force'applied'bymagnet113,vtliedevice will now be held against furtheroperation. fj 5 In'order to-reset thegde'vice-b piotingthe Zinertia unit'downwardly' toward fmag'net-`11l2-y andv so' .-refenga'ging'. themagnetic couple, I provide a "I efpsff 12a/may smear-tea. y

reciprocating plunger e material tendency 'to 'shiftiwith changingpressures resultingjfromndjustment ofthe device.. The leaf sprng1-09.Vis maintained inexble, except inrfaj'plane substantially;

normal toits majorlsurfaceszj i Y Y `A vibration responsivezswitch'constructed in accor-,cl-

r ance Vwith' Figs. l4..was' tested on a vibrationffcalibrator, theswitch .being-.adjustedto actuate .at LOG, actuation. beingfeiectedatffvarious-.frequencies'ranging from 25 to ,200 .cycles per second.v.Results of such testfare as follows:

1 z req'uency l e A Acceleration at actuation.

(cyclesper' second): point (in Gfs) Y 25 T.'.f..l nagmmms. 0:97.:

VIt will thus be inthe onefdegree of freedom in motion necessaryfordis-g engagement of the magnetic means, is ,essential if suchflatlrespons'eiis to be obtained The bodyios preferably' of iron, rgrama nat,'anni plated toprovide a .thin surface coating of soft metal,v

preferably silver. Before nal assembly,Y the contact surfaces betweenthe inertiamember 105 and the magnet Y V112areworn-in by maintaining alight face-to-face contact Yandvrvvibrating at a relatively highfrequencyto` provide a continuouschattering impact; 1 In this man-Q ner,.the at mating faces ofthe paramagnetic body` and `n'iaglwt .are made tomatch eachother asV closely .as

e seen r theI device exhibits'essentiallylllat V response within thisfrequencyr range. 'I have found that rigid restraint of the .moving'system` ofthe device, except Wea possible so that the same magneticforce will result upon each engagement of the magnetic means. Ashereinbefore pointed out, it is highly desirable to exclude all dustparticles and the like from possible contact with the magnetic means.For this purpose, I provide the felt sealing washers 127 and 134 toprevent infiltration of dust and the like into the casing 128. It willbe understood that the casing closely embraces the members 102, 103 and104 and is secured thereto by closely spaced machine screws as shown inFig. 4 so that a sealing contact is maintained between the casing andthese members.

Acceleration responsive devices can be built in accordance with Figs.1-4 to have a wide range of response. Thus, it is possible to obtainrepeatably accurate response at acceleration levels as low as .0l G.Tests have been run on such devices at .05 G and 300 cycles per second,in which precise actuation was obtained with a vibratory amplitude aslow as 5 microinches.

While I have shown the control device as a conventional snap switch, itwill be understood that such device may be a conventional hydraulicvalve or other suitable mechanism, in accordance with the purpose of theparticular unit.

The invention is also adapted for use as a peak accelerometer either asshown or in simpler form without the switch 120, the operation being asdescribed with reference to Figs. 1-4. For most applications, the impactcaused by engagement of inertia member 105 with latching magnet i113,being clearly audible, serves as an indication that the predeterminedacceleration has occurred. Where it is impractical to depend upon thesound made by actuation of the device, the casing 128 may be providedwith a window-to allow observation of the inertia unit.

A modication of the device constructed for operation in response toacceleration at a given frequency is shown in Fig. 5. Here, the base201, support 202, end member 204, shaft 207, inertia member 205, andmagnets 212 and 213 are constructed and arranged in the same manner asthe corresponding parts in Figs. 1 4, it being understood that theportion of the device not seen in Fig. 5 may be constructed inaccordance with Figs. l4. Inertia element 205 is provided with van endslot in which is iixed one end ofva leaf spring 2059', the other end ofthe spring being xed to an additional mass 2051. The spring 205e andadditional mass l205b constitute a resonant system for amplifying theforce produced on the inertia unit by vibratory acceleration near theresonant frequency..

Thus, with ferromagnetic member 205 engaged with restraining magnet 212,the biasing means is adjusted to preselect a given magnitudeyofacceleration for actuation of the device. The resonant system comprisinglspring 205a and supplementary mass 205b allows the device to berelatively insensitive to vibratory acceleration at frequencies diierentfrom .the resonant frequency of that system. Upon occurrence of thepredetermined acceleration at the resonant frequency, the forces actingupon the inertia unit are unbalancedin al sense tending to move member205 upwardly, the magnetic couple comprising member 205 and magnet 212is disengaged, and the force of the biasing means as spring 122, Fig. l,is effective to pivot the inertia unit upwardly to engage member 205with latching magnet 213.

Referring to Fig. l, it is evident that the motion of the inertia unitis angular about the pivot axis between blocks 110 and 111, rather thanlinear in character. But, because the total angular travel is small, therelations aiecting sensitivity of the device may be treated on a linearbasis involving mass, force and leverage ratios as well as in terms ofmoment of inertia Vand torque. The device of Fig. 1 is sensitive to theresultant vertical downward acceleration acting through a point to theright (as viewed) of the pivot and at a distance from the pivot equal tothe radius of gyration. When most of the mass d of the inertia unit isconcentrated in' member 105, this point will fall close to the center ofgravity of member 10S. When, on the other hand, the inertia unit isbalanced by increasing the mass of lever 118 and decreasing the mass ofmember 105, the center of gravity may be made to fall at the pivot axiscausing the device to be insensitive to linear acceleration. It may thenbe usedy as an angular accelerometer, sensitive only to angularacceleration about the pivot axis, the sensitivity being dependent onthe moment of inertia of the inertia unit.

When the device is mounted in any given orientation on a machine, thegravitational component, which is equivalent to acceleration, isbalanced out (while the machine is not running) by determining thesetting of the adjustable biasing means at which thev device willactuate while not being subjected to any material vibration.Measurements are then made away from this setting as a z'ero referencefor vibratory acceleration. The sensitivity of the device to gravity, orresponse at zero frequency, adds utility to the device for such` purposeas determining when an aircraft in4 ight has exceeded a predeterminedsafe G loading. Sensitivity to gravity also permits accurate calibrationof the adjusting means by noting the difference in settings of theadjusting means necessary to actuate the device with the base plane(that is, the plane in which member 101 lies) vertical and with thebase'plane horizontal, this difference correspond'- ing to anacceleration of 1 G. Here, acceleration in Gs is dened as the linearacceleration divided by the acceleration of gravity.

The biasing means including spring 122, Fig. l, serves to overcome boththe restraining force of the magnetic couple and the weight of theinertia unit. To set for a'given peak vibratory acceleration, thesensitivity of the adjusting means is related to the leverage ratios,the number of turns per inch of screw 124, the effective mass ofth'einertia unit including member I105 and the spring rate, which may begiven in pounds per inch, of the spring 122. Sensitivity of theadjusting means is independent of the restraining force of the magneticcouple, which restraining force aiects the zero reference setting andthe spring energy available to move the inertia unit and actuate theswitch operating pin 119, after the magnetic couple is disengaged. Thus,the spring rate, and the adjusting screw sensitivity are determined forthe given mass of the inertia unit. A v

For example, in a device constructed in accordance with Fig. 1 employinga leverage ratio of 5:1, an adjusting screw of 32 threads per inch andan eiective mass (at a point over the magnetic couple) of 0.079 pound,an additional spring force of 0.4 pound was required to balance theweight of the inertia unit. With the screw 124 providing a travel of1/32 inch per turn of the screw,

`the corresponding spring rate to obtain an adjustment sensitivity ofone revolution of adjusting knob 129 per G was 12.8 pounds per inch. Therestraining force of the magnetic couple, however, was approximately 0.5pound, or 2.5 pounds on the spring side of the lever, corresponding to atotal spring deflection of 0.195 inch or about V6M: turns of theadjusting screw. The lrelations between mass and the required springrate for a given sensitivity may be calculated by similar-.methods forany given coniiguration of the device.

In the embodiment of Fig. 1, the magnetic couple is formed by permanentmagnet 112 yand inertia memiber 105. Magnet 112 is preferably ofaluminum-nickelcobalteiron alloy (Alnico), While member 10S is ofmagnetically soft iron silver-plated to resist corrosion and provide anon-wearing impact-resistant surface. The thickness of the plating isequivalent, magnetically, to a small air gap which reduces therestraining force of the magnetic'couple but, if suiiiciently thin, doesnot affect satisfactory operation. An air gap may be purposely includedto improve repeatability in embodiments of the device where dustparticles, oil, etc., are apt to deposit on the contacting sur-faces ofthe magnetic couple.

'Ehe permanent. magnet may be. mounted oni the inertia unit if desired,`the other member of the couple, being either a soft ferromagnetic bodyor ar second permanent magnet, then being rigidly attached to thesupport. AThe magnetic couple should. have all pole faces -in a close uxlinkage when engaged., It is essential that the separation, if any, ofthe ferromagnetic elements of the couple be.A precisely maintained foreach` successive engagement. v The embodiment ofthe invention seen inFig, i,A in cludingsingle-pole-double-throw snap switch 120, may bewired. through cable'136 into. warning, control, or indicating circuits;to actuate a warning signal or shut down a machine when vibrationexceeds a predetermined. safe value..A The. zero setting is determinedwith. the machine not. The device is then reset and adjusted toY actuatewith the machine. running nonnally, the normal vibration then beingdetermined from the. diierence, in the-two on calibrated dial 13,0.,Head 1.29 iS. then. turned an additional .amount in a. directiondecreesA ing the biasing 4force of spring 122-, to, provide .a desired'safety factor. Reset pin 13-1. is then depressedV to ref engage themagnetic couple, .the device thus being set to actuate Whenever themachine.. is .subjected to vibration in excess. of the.. safetyv factor.

I claim:

l. In an acceleration responsive device, the combina: tion of a baselmember; mounting means comprising a leaf spring and a pair of blocksrigidly -secured Vto oppoe site faces of said spring and offset one fromthe other with adjacent corner portions of the two blocks slightlyoverlapped, one of 'said blocks .being rigidly securedr to said basemember; a magnetic couple, a rigid inertia unit including the Vother ofsaid blocks and one element of said magnetic couple, the otherelement ofsaid magnetic couple lbeing rigidly secured to said base member; a rigidlever' iixed to said other block and extending away from said magneticcouple; resilient means acting on said lever and `disposed to apply abiasingr force-thereto toward said base member and tending both todisengage said magnetic couple 'and to urge said blocks toward cachother, and meansfor adjustingisaid resilient means to determine'saidbiasing force and so predetermine the acceleration valueV effective todisengage said magnetic couple.

2. Vin an acceleration responsive device, the combination of a support;mounting means comprising a leaf `spring and a pair of blocks `rigidly-xed one 'to each Vface of said spring with adjacent corners of saidblocks in-subs'tanti'al alignment, Y one of said blocks rbeing rigidlysecured tofesaid support; a pair of spaced parallel shafts secured tothe other ofsaid blocks and extending above said support; an inertiaelement rigidly fixed to the ends of said shafts, said other bloc-k,said shafts and said element constituting a rigid inertia unitconstrained by said mounting means to one degree of freedom in motionrelative to said support; a ferromagneticmember xed to said support anddisposed Ito be engageable by said inertia element as `a result ofmotion in said one degree of free-V dom, said ferromagnetic member andsaid inertia element constituting a magnetic couple; resilient meansconnected to said mounting means and `disposed to apply a biasingforce.' toi the sian-tetu. ai directiontendiug: te disensage Saidmagnetic couple; and means. for adjusting said. resilient-Y Ineans todetermine Said; biasing terse and thusprrzedeter-J mine the accelerationvalue edeetive to disensase` saidrnagnetio couple. i

3l. In; an acceleration responsive. device, thecombinaf:

tion ofy a support ladapted to be mounted so; as; to be. sub: ject toacceleration, an inertial mass, .means for mount# ing said mass onl saidsupport, 'saidmounting meansi having a very high resistance to movementof the. mass.

in .all except one plane, to permit only one degree of freedom of.motion of the mass relative to: the support, magnetici meansoperatively associated with said mass to; .exert a force thereon tendingto hold the mass ini a! xed position with respect t'o the support tocauseV the mass to move therewith, spring biasing meansoperai..l

tively associated with said mass to urge the vmass away.

from said support with a force tending to cause motion` Vis at saidparticular frequency. Y

4. In an acceleration responsive device having a support and an inertiaelement with a magnetic couple exerting aforee between said support andelement; means for mounting said inertia element upon said supportfor'piv* tal movement in `a single degree of' freedom 'relativeto saidsupport,'s aid means comprising a rst block rigid with said frame, avflat sheet-like element having a por-` tion yrigidly secured to asurface of said rst block and Y having a second portion projectingbeyond an edgeof said Surface, a second block. for carrying the inertiaelement and having a surface secured tothe second portion' of said flatelement, said blocks being secured to opposite sides of said element`and having parallel corner edges spaced. only by the thickness of saidelement i References Cited-in the file of this patent UNITED STATESPATENTS

